Bismaleimides have been utilized with epoxy monomers and aromatic amines to provide polyimide molding compositions with high heat distortion temperatures, as disclosed in U.S. Pat. Nos. 4,294,723 and 4,294,877. A disadvantage that is characteristic of these molding compositions is that they have a slow cure rate, typically requiring about 0.5-2 hours to cure.
Maleic anhydride has been known to react rapidly with aliphatic vinyl ethers, as disclosed by Leonard, ed. Vinyl and Diene Monomers. Vol. 24, Part I, NY: Wiley interscience, 1970, pp. 399-401. However, the cured product obtained with maleimide and aliphatic vinyl ethers are not attractive because of low heat distortion temperatures. In addition, these aliphatic vinyl ethers are liquid at room temperature and are not amenable to the formulation of solid molding compositions, making such compositions difficult to process into finished products.
The present invention is based on the discovery that maleimides copolymerize rapidly with aromatic vinyl ethers. The resulting copolymers have high oxidative stability and high heat distortion temperatures which overcome the disadvantages characteristic of polyimide molding compositions known to the art.